Electric arc furnace dust hereinafter referred to as “EAFD” is produced by the steel industry and is classified into two major categories. One category is dust that is produced from steel mills and the other is dust produced from steel foundries. Typically EAFD is obtained from “bag houses” but may be recovered from cyclones and electro-static precipitators.
A number of methods have been used to extract valuable components, as for example Zinc, from EAFD. However, it is considered to be more economical to use the EAFD in its raw state. One problem is that even after the recovery of some of the metals, the remaining dust must be disposed of in a disposal site or the like.
One approach to reduce the disposal cost for EAFD is disclosed in our earlier U.S. Pat. No. 5,557,031, entitled “Use of Electric Arc Furnace By-Product in Concrete” that was developed at the Department of Civil Engineering, King Saud University, Riyadh, Saudi Arabia. As disclosed therein, EAFD may be used as a partial replacement or additive for cement to provide retardation and enhance properties including corrosion inhibiting in concrete bodies. As stated in the patent, under appropriate conditions EAFD confers enhanced properties to the end product. Therefore, EAFD can be disposed of in an environmentally more attractive manner. Moreover, benefits result not only from savings in cement use, but also from savings in the operation of electric arc furnaces and by reducing EAFD disposal costs. The U.S. Pat. No. 5,557,031 is incorporated herein in its entirety by reference.
It has also been recognized that hot weather can cause problems in working with concrete and that such problems increase as temperatures rise. For example, it has been reported that it may be necessary to make adjustments to a concrete mix as the weather warms because an everyday mix can begin to perform differently as temperatures rise above 23° C. (75° F.). It has also been recognized that for hot weather concreting, hot weather is a combination of the following weather conditions; high ambient temperature, low relative humidity, solar radiation and wind.
In the Middle East and some parts of the United States ambient temperatures of about 32° C. to about 45° C. are frequently encountered during the summer months. For example, in 1913 in Death Valley, Calif. a temperature of 134° F. (56.6° C.) was recorded. Problems associated with extreme heat i.e. 32° C. (90° F.) to 40 or 45° C. (104°-113° F.) or greater include increased water demand, increased rate of slump loss, increased rate of setting, increased tendency for plastic-shrinkage cracking and increased difficulty in controlling entrained air content. For hardened concrete, the main problem is the decreased long-term strength.
Authorities in concrete technology such as those at the American Concrete Institute (ACI) and Portland Cement Association (PCA) recommend cooling concrete as low as possible in order to obtain good quality concrete in hot weather. In addition some specifications require that when placed, concrete should have a temperature of less than 29° C. (84° F.) to 32° C. (90° F.). Therefore, in areas of extreme temperature, ice or chilled water is added to a hydraulic cement, aggregate and water mix. Further, in adding ice, it is important to use crushed, shaved or chipped ice to ensure that all of the ice melts before mixing is completed. Reducing temperature of a concrete mix adds substantial cost to the process.
Set retarding/water-reducing admixtures are sometimes used to counteract some of the negative impacts of hot weather on fresh concrete, particularly the rapid setting caused by high temperatures. Water-reducing admixtures can help curb slump loss without effecting the water demand of the mix, however, chemical admixtures are conditional on cement type and require care in adjusting dosage. Admixtures that increase the bleeding rate can help counteract surface drying, but may also require additional consolidation after the majority of bleeding has subsided.
An early approach to a method for cementing in environments having elevated temperatures is disclosed in a U.S. Pat. No. 3,856,541 of Martin. As disclosed therein a water-soluble hydroxy carboxylic acid or salt thereof and boric acid or a water soluble salt thereof are mixed with an aqueous hydraulic cement slurry to increase the normal setting time. A water-soluble boron containing hydroxyl carboxylic acid or salt thereof can be substituted for the aforementioned mixture.
It is presently believed that a method in accordance with the present invention will provide a concrete with improved strength and slump retention capability, provide a more economical solution to a problem of concreting in a high temperature environment, increase the use of EAFD, thus leading to a clean environment and eliminate the need for chilled water or ice in concreting at elevated temperatures.